This invention relates to a control device for striper units in circular knitting machines, in particular double-cylinder hosiery knitting machines.
It is known that a striper unit in a double-cylinder circular knitting machine, such as the one disclosed in U.S. Pat. No. 3,605,444 to Francesco Lonati, comprises a plurality of thread fingers for each machine feed, the various thread fingers being selectively movable to and from the needle cylinders in order to feed, or respectively remove, the respective threads every time that the knitting process requires replacement of a given thread with another thread of a different nature, denier or color. Associated with the thread fingers are one or more thread cutting means, which effect the cutting of the thread upon removal of the latter from the knitting cycle, and one or more thread gripping means, which are sometimes made integral with the cutting members, e.g. as disclosed in U.S. Pat. No. 3,552,149 to Francesco Lonati, which hold back the cut thread until it is re-inserted in the knitting cycle.
Each striper unit may comprise up to five, six, or more thread fingers, for the movement whereof a control device is provided which is adapted for controlling the movement of the respective thread cutting and gripping means. The control devices currently known in the art have a very complex construction and a fairly small degree of versatility. A typical control device would comprise, in fact, a plurality of arcuate control levers rigidly mounted to a control shaft rocking about its own axis, which arcuate levers are adapted to engage and selectively advance respective toothed profile disks, to which other, but cam profiled, disks are rigid, whereby the movements of the respective thread fingers and thread cutting and gripping means are controlled by means of a lever and Bowden cable type of linkage system. To cause the simultaneous movement of the arcuate control levers to reflect in a selective action on the disks, provision is made for the presence of a rod having plural side notches and interposed projections of different heights, said rod being displaceable parallel to itself and influencing with its notches and projections, in conformity with its height, the various levers in their rocking motion, such that only one of them, namely the one selected in accordance with the program, becomes active on its related toothed disk. The displacement of the selecting rod is provided by a stepped sector, or segment, which steps are operative to engage an arm protruding from said rod according to necessity, the sector being controlled to rotate by the machine program.
A first drawback of such a control device resides in its inability to provide for simultaneous insertion in the knitting cycle of two or more thread fingers, as is the case with some special patterned knitwork. It is sometimes possible, with some special provisions, to obtain two simultaneous selections, but this is only limited to two particular thread fingers, i.e. it is impossible to combine at will the thread fingers that are to be brought into operation simultaneously.
Another drawback is that the toothed disks, being advanced by means of levers, must be provided with closely spaced teeth, e.g. for a total of six teeth, which restricts to a very small arc the extension of the cams controlling, at each advance increment, the thread fingers and cutting and gripping members. It follows that a structure of this type cannot meet the modern requirements for fast knitting, because if the disks are actuated too rapidly it may happen that the short cam profile thereof cannot be correctly followed by the corresponding linkages which control the thread fingers and the cutting and gripping members.
Moreover, the arrangement of several cam disks at each thread finger and cutting and gripping means, each disk having a distinctive peripheral contour, and the arrangement of several identical profiles on the same disk, owing to the short rotation imparted with each actuation, involve constructional difficulties and problems in timing the disks one with respect to the other, any minimal error in construction and timing being apt to reflect in a machine malfunctioning.
Such drawbacks are not substantially obviated by the device disclosed in U.S. Pat. No. 3,888,094 to Francesco Lonati. This device still provides for the presence of an arcuate lever for advancing a corresponding toothed disk, although the lever is actuated by a rotary member, in a manner similar to a crank-connecting rod system. The rotary member can be coupled and uncoupled controllably, at predetermined times, to a shaft held in constant rotation by the action of the machine drive means. In this device, a degree of constructional simplification is achieved, as is a more accurate intervention with respect to the previously described device, but the device still retains the problems, already mentioned above, relating to fast advance by very short portions of the toothed disks, as well as the timing problem, when several similar units are utilized for multiple thread fingers.
German Patent No. 973,500 to Gottlieb Eppinger K.G. discloses instead a device wherein actuation of a secondary thread finger, in or out of the knitting cycle, is obtained through a 180.degree. respective rotation of a cam disk which can be coupled and uncoupled controllably to and from a constantly rotating shaft, and is followed by one end of a rocking lever, to the opposite end whereof there is a hooked a thread finger actuating cable. More in detail, the cam disk can be coupled and uncoupled by displacing the disk itself axially, the disk being idle mounted to the shaft and rigid with a coupling element, engageable by axial movement with a mating coupling member which remains rigid with the rotating shaft. Control is achieved through a rocking lever controlled by the machine programming chain, which lever, in one position, is active to release the coupling element under the action of a spring in engagement relationship with the coupling member which is rigid with the shaft, and in another position, disengages it from that member against the spring bias.
This device affords a more accurate intervention, since it has a 180.degree. arc available for each control actuation, whereby it is also suitable for use in high speed machines. However, it is unsuitable for application where selective operation of several thread fingers is required, because each of these would then require an axial coupling system, with its attendant spring and control lever, of its own, thus rendering the device a bulky one, which is unpractical on machines which are known to allow but a limited space for the various controls.